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 $212.82   10.179%   $234.4829   $234.48   $234.50   $234.50  
  Purchase #2 $20.97   12.344%   $23.5585   $23.56   $23.55   $23.60  
  Purchase #3 $66.82   10.519%   $73.8488   $73.85   $73.85   $73.80  
  Purchase #4 $226.59   7.382%   $243.3169   $243.32   $243.30   $243.30  
  Purchase #5 $217.74   13.430%   $246.9825   $246.98   $247.00   $247.00  
  Purchase #6 $24.59   5.201%   $25.8689   $25.87   $25.85   $25.90  
  Purchase #7 $159.66   12.499%   $179.6159   $179.62   $179.60   $179.60  
  7 purchase totals = $929.19       $1,027.6744   $1,027.68   $1,027.65   $1,027.70