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 $198.79   13.620%   $225.8652   $225.87   $225.85   $225.90  
  Purchase #2 $171.63   5.437%   $180.9615   $180.96   $180.95   $181.00  
  Purchase #3 $244.56   6.326%   $260.0309   $260.03   $260.05   $260.00  
  Purchase #4 $67.38   13.578%   $76.5289   $76.53   $76.55   $76.50  
  Purchase #5 $160.62   11.710%   $179.4286   $179.43   $179.45   $179.40  
  Purchase #6 $184.62   9.331%   $201.8469   $201.85   $201.85   $201.80  
  Purchase #7 $77.95   11.618%   $87.0062   $87.01   $87.00   $87.00  
  7 purchase totals = $1,105.55       $1,211.6682   $1,211.68   $1,211.70   $1,211.60