Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $173.31   13.473%   $196.6601   $196.66   $196.65   $196.70  
  Purchase #2 $154.78   12.131%   $173.5564   $173.56   $173.55   $173.60  
  Purchase #3 $24.86   11.780%   $27.7885   $27.79   $27.80   $27.80  
  Purchase #4 $185.91   9.700%   $203.9433   $203.94   $203.95   $203.90  
  Purchase #5 $184.54   10.651%   $204.1954   $204.20   $204.20   $204.20  
  Purchase #6 $110.79   12.299%   $124.4161   $124.42   $124.40   $124.40  
  Purchase #7 $216.55   13.132%   $244.9873   $244.99   $245.00   $245.00  
  7 purchase totals = $1,050.74       $1,175.5471   $1,175.56   $1,175.55   $1,175.60