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 $38.70   6.761%   $41.3165   $41.32   $41.30   $41.30  
  Purchase #2 $195.78   13.829%   $222.8544   $222.85   $222.85   $222.90  
  Purchase #3 $48.94   11.540%   $54.5877   $54.59   $54.60   $54.60  
  Purchase #4 $202.36   13.703%   $230.0894   $230.09   $230.10   $230.10  
  Purchase #5 $121.56   4.125%   $126.5744   $126.57   $126.55   $126.60  
  Purchase #6 $200.72   12.691%   $226.1934   $226.19   $226.20   $226.20  
  Purchase #7 $201.96   13.838%   $229.9072   $229.91   $229.90   $229.90  
  7 purchase totals = $1,010.02       $1,131.5230   $1,131.52   $1,131.50   $1,131.60