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 $134.28   12.467%   $151.0207   $151.02   $151.00   $151.00  
  Purchase #2 $244.35   5.783%   $258.4808   $258.48   $258.50   $258.50  
  Purchase #3 $201.78   8.368%   $218.665   $218.67   $218.65   $218.70  
  Purchase #4 $54.36   9.331%   $59.4323   $59.43   $59.45   $59.40  
  Purchase #5 $88.26   6.793%   $94.2555   $94.26   $94.25   $94.30  
  Purchase #6 $204.95   8.394%   $222.1535   $222.15   $222.15   $222.20  
  Purchase #7 $60.72   13.293%   $68.7915   $68.79   $68.80   $68.80  
  7 purchase totals = $988.70       $1,072.7993   $1,072.80   $1,072.80   $1,072.90