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 $75.41   3.413%   $77.9837   $77.98   $78.00   $78.00  
  Purchase #2 $218.48   10.616%   $241.6738   $241.67   $241.65   $241.70  
  Purchase #3 $70.46   5.424%   $74.2818   $74.28   $74.30   $74.30  
  Purchase #4 $66.45   12.551%   $74.7901   $74.79   $74.80   $74.80  
  Purchase #5 $93.45   7.216%   $100.1934   $100.19   $100.20   $100.20  
  Purchase #6 $212.66   6.548%   $226.585   $226.59   $226.60   $226.60  
  Purchase #7 $122.67   5.668%   $129.6229   $129.62   $129.60   $129.60  
  7 purchase totals = $859.58       $925.1307   $925.12   $925.15   $925.20