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 $201.41   12.301%   $226.1854   $226.19   $226.20   $226.20  
  Purchase #2 $23.35   6.816%   $24.9415   $24.94   $24.95   $24.90  
  Purchase #3 $243.53   12.657%   $274.3536   $274.35   $274.35   $274.40  
  Purchase #4 $207.29   6.494%   $220.7514   $220.75   $220.75   $220.80  
  Purchase #5 $191.92   3.546%   $198.7255   $198.73   $198.75   $198.70  
  Purchase #6 $224.52   3.871%   $233.2112   $233.21   $233.20   $233.20  
  Purchase #7 $227.94   11.349%   $253.8089   $253.81   $253.80   $253.80  
  7 purchase totals = $1,319.96       $1,431.9775   $1,431.98   $1,432.00   $1,432.00