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 $154.27   9.405%   $168.7791   $168.78   $168.80   $168.80  
  Purchase #2 $227.41   11.653%   $253.9101   $253.91   $253.90   $253.90  
  Purchase #3 $78.56   12.277%   $88.2048   $88.20   $88.20   $88.20  
  Purchase #4 $244.39   13.424%   $277.1969   $277.20   $277.20   $277.20  
  Purchase #5 $238.72   9.672%   $261.809   $261.81   $261.80   $261.80  
  Purchase #6 $162.52   11.353%   $180.9709   $180.97   $180.95   $181.00  
  Purchase #7 $98.66   4.237%   $102.8402   $102.84   $102.85   $102.80  
  7 purchase totals = $1,204.53       $1,333.7110   $1,333.71   $1,333.70   $1,333.70