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 $85.64   9.683%   $93.9325   $93.93   $93.95   $93.90  
  Purchase #2 $228.79   11.817%   $255.8261   $255.83   $255.85   $255.80  
  Purchase #3 $147.79   9.267%   $161.4857   $161.49   $161.50   $161.50  
  Purchase #4 $222.27   10.124%   $244.7726   $244.77   $244.75   $244.80  
  Purchase #5 $203.62   9.818%   $223.6114   $223.61   $223.60   $223.60  
  Purchase #6 $99.80   10.357%   $110.1363   $110.14   $110.15   $110.10  
  Purchase #7 $17.25   4.280%   $17.9883   $17.99   $18.00   $18.00  
  7 purchase totals = $1,005.16       $1,107.7529   $1,107.76   $1,107.80   $1,107.70