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 $48.94   12.574%   $55.0937   $55.09   $55.10   $55.10  
  Purchase #2 $145.67   8.413%   $157.9252   $157.93   $157.95   $157.90  
  Purchase #3 $177.53   5.595%   $187.4628   $187.46   $187.45   $187.50  
  Purchase #4 $198.70   3.640%   $205.9327   $205.93   $205.95   $205.90  
  Purchase #5 $131.84   13.494%   $149.6305   $149.63   $149.65   $149.60  
  Purchase #6 $184.74   5.642%   $195.163   $195.16   $195.15   $195.20  
  Purchase #7 $74.72   12.432%   $84.0092   $84.01   $84.00   $84.00  
  7 purchase totals = $962.14       $1,035.2171   $1,035.21   $1,035.25   $1,035.20