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 $93.56   12.174%   $104.95   $104.95   $104.95   $105.00  
  Purchase #2 $223.75   3.861%   $232.389   $232.39   $232.40   $232.40  
  Purchase #3 $232.33   4.725%   $243.3076   $243.31   $243.30   $243.30  
  Purchase #4 $250.45   10.185%   $275.9583   $275.96   $275.95   $276.00  
  Purchase #5 $101.72   8.221%   $110.0824   $110.08   $110.10   $110.10  
  Purchase #6 $190.96   6.284%   $202.9599   $202.96   $202.95   $203.00  
  Purchase #7 $6.29   10.460%   $6.9479   $6.95   $6.95   $6.90  
  7 purchase totals = $1,099.06       $1,176.5951   $1,176.60   $1,176.60   $1,176.70