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 $85.44   10.410%   $94.3343   $94.33   $94.35   $94.30  
  Purchase #2 $129.78   6.589%   $138.3312   $138.33   $138.35   $138.30  
  Purchase #3 $195.31   11.717%   $218.1945   $218.19   $218.20   $218.20  
  Purchase #4 $205.35   13.318%   $232.6985   $232.70   $232.70   $232.70  
  Purchase #5 $245.50   11.610%   $274.0026   $274.00   $274.00   $274.00  
  Purchase #6 $77.92   3.410%   $80.5771   $80.58   $80.60   $80.60  
  Purchase #7 $8.89   10.523%   $9.8255   $9.83   $9.85   $9.80  
  7 purchase totals = $948.19       $1,047.9637   $1,047.96   $1,048.05   $1,047.90