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 $96.61   11.717%   $107.9298   $107.93   $107.95   $107.90  
  Purchase #2 $239.78   10.369%   $264.6428   $264.64   $264.65   $264.60  
  Purchase #3 $64.98   13.536%   $73.7757   $73.78   $73.80   $73.80  
  Purchase #4 $102.34   3.790%   $106.2187   $106.22   $106.20   $106.20  
  Purchase #5 $116.82   13.240%   $132.287   $132.29   $132.30   $132.30  
  Purchase #6 $54.85   11.394%   $61.0996   $61.10   $61.10   $61.10  
  Purchase #7 $239.88   12.263%   $269.2965   $269.30   $269.30   $269.30  
  7 purchase totals = $915.26       $1,015.2501   $1,015.26   $1,015.30   $1,015.20