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 $88.88   9.717%   $97.5165   $97.52   $97.50   $97.50  
  Purchase #2 $236.43   4.783%   $247.7384   $247.74   $247.75   $247.70  
  Purchase #3 $230.57   11.739%   $257.6366   $257.64   $257.65   $257.60  
  Purchase #4 $238.70   11.591%   $266.3677   $266.37   $266.35   $266.40  
  Purchase #5 $240.74   4.728%   $252.1222   $252.12   $252.10   $252.10  
  Purchase #6 $232.57   9.402%   $254.4362   $254.44   $254.45   $254.40  
  Purchase #7 $59.86   11.847%   $66.9516   $66.95   $66.95   $67.00  
  7 purchase totals = $1,327.75       $1,442.7692   $1,442.78   $1,442.75   $1,442.70