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 $171.79   7.117%   $184.0163   $184.02   $184.00   $184.00  
  Purchase #2 $204.90   10.405%   $226.2198   $226.22   $226.20   $226.20  
  Purchase #3 $49.94   7.404%   $53.6376   $53.64   $53.65   $53.60  
  Purchase #4 $243.41   9.312%   $266.0763   $266.08   $266.10   $266.10  
  Purchase #5 $69.64   4.351%   $72.67   $72.67   $72.65   $72.70  
  Purchase #6 $23.72   9.599%   $25.9969   $26.00   $26.00   $26.00  
  Purchase #7 $20.88   7.835%   $22.5159   $22.52   $22.50   $22.50  
  7 purchase totals = $784.28       $851.1328   $851.15   $851.10   $851.10