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 $223.94   8.500%   $242.9749   $242.97   $242.95   $243.00  
  Purchase #2 $119.39   10.224%   $131.5964   $131.60   $131.60   $131.60  
  Purchase #3 $113.95   7.373%   $122.3515   $122.35   $122.35   $122.40  
  Purchase #4 $56.51   6.353%   $60.1001   $60.10   $60.10   $60.10  
  Purchase #5 $211.60   8.257%   $229.0718   $229.07   $229.05   $229.10  
  Purchase #6 $158.91   9.379%   $173.8142   $173.81   $173.80   $173.80  
  Purchase #7 $76.54   8.613%   $83.1324   $83.13   $83.15   $83.10  
  7 purchase totals = $960.84       $1,043.0413   $1,043.03   $1,043.00   $1,043.10