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 $129.29   4.149%   $134.6542   $134.65   $134.65   $134.70  
  Purchase #2 $202.42   5.789%   $214.1381   $214.14   $214.15   $214.10  
  Purchase #3 $133.75   11.458%   $149.0751   $149.08   $149.10   $149.10  
  Purchase #4 $144.66   3.663%   $149.9589   $149.96   $149.95   $150.00  
  Purchase #5 $200.83   8.257%   $217.4125   $217.41   $217.40   $217.40  
  Purchase #6 $227.80   9.456%   $249.3408   $249.34   $249.35   $249.30  
  Purchase #7 $88.91   7.770%   $95.8183   $95.82   $95.80   $95.80  
  7 purchase totals = $1,127.66       $1,210.3979   $1,210.40   $1,210.40   $1,210.40