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 $66.80   10.807%   $74.0191   $74.02   $74.00   $74.00  
  Purchase #2 $138.43   8.836%   $150.6617   $150.66   $150.65   $150.70  
  Purchase #3 $80.82   12.447%   $90.8797   $90.88   $90.90   $90.90  
  Purchase #4 $133.45   7.317%   $143.2145   $143.21   $143.20   $143.20  
  Purchase #5 $204.89   10.412%   $226.2231   $226.22   $226.20   $226.20  
  Purchase #6 $22.86   8.577%   $24.8207   $24.82   $24.80   $24.80  
  Purchase #7 $50.33   5.592%   $53.1445   $53.14   $53.15   $53.10  
  7 purchase totals = $697.58       $762.9633   $762.95   $762.90   $762.90