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 $31.82   9.192%   $34.7449   $34.74   $34.75   $34.70  
  Purchase #2 $184.60   4.709%   $193.2928   $193.29   $193.30   $193.30  
  Purchase #3 $60.98   10.433%   $67.342   $67.34   $67.35   $67.30  
  Purchase #4 $69.56   5.173%   $73.1583   $73.16   $73.15   $73.20  
  Purchase #5 $142.79   5.363%   $150.4478   $150.45   $150.45   $150.40  
  Purchase #6 $87.34   12.205%   $97.9998   $98.00   $98.00   $98.00  
  Purchase #7 $210.38   7.523%   $226.2069   $226.21   $226.20   $226.20  
  7 purchase totals = $787.47       $843.1925   $843.19   $843.20   $843.10