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 $53.50   7.604%   $57.5681   $57.57   $57.55   $57.60  
  Purchase #2 $139.98   9.124%   $152.7518   $152.75   $152.75   $152.80  
  Purchase #3 $43.85   7.688%   $47.2212   $47.22   $47.20   $47.20  
  Purchase #4 $105.50   12.549%   $118.7392   $118.74   $118.75   $118.70  
  Purchase #5 $53.43   13.362%   $60.5693   $60.57   $60.55   $60.60  
  Purchase #6 $184.82   7.311%   $198.3322   $198.33   $198.35   $198.30  
  Purchase #7 $214.71   11.217%   $238.794   $238.79   $238.80   $238.80  
  7 purchase totals = $795.79       $873.9758   $873.97   $873.95   $874.00