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 $40.28   7.824%   $43.4315   $43.43   $43.45   $43.40  
  Purchase #2 $149.33   7.370%   $160.3356   $160.34   $160.35   $160.30  
  Purchase #3 $47.45   5.802%   $50.203   $50.20   $50.20   $50.20  
  Purchase #4 $118.65   9.231%   $129.6026   $129.60   $129.60   $129.60  
  Purchase #5 $230.47   12.318%   $258.8593   $258.86   $258.85   $258.90  
  Purchase #6 $222.66   5.778%   $235.5253   $235.53   $235.55   $235.50  
  Purchase #7 $134.34   8.234%   $145.4016   $145.40   $145.40   $145.40  
  7 purchase totals = $943.18       $1,023.3589   $1,023.36   $1,023.40   $1,023.30