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 $232.82   8.460%   $252.5166   $252.52   $252.50   $252.50  
  Purchase #2 $112.81   10.563%   $124.7261   $124.73   $124.75   $124.70  
  Purchase #3 $62.93   4.276%   $65.6209   $65.62   $65.60   $65.60  
  Purchase #4 $184.93   8.153%   $200.0073   $200.01   $200.00   $200.00  
  Purchase #5 $112.94   11.251%   $125.6469   $125.65   $125.65   $125.60  
  Purchase #6 $90.96   6.418%   $96.7978   $96.80   $96.80   $96.80  
  Purchase #7 $59.84   6.751%   $63.8798   $63.88   $63.90   $63.90  
  7 purchase totals = $857.23       $929.1954   $929.21   $929.20   $929.10