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 $186.53   8.196%   $201.818   $201.82   $201.80   $201.80  
  Purchase #2 $194.74   4.157%   $202.8353   $202.84   $202.85   $202.80  
  Purchase #3 $155.33   10.663%   $171.8928   $171.89   $171.90   $171.90  
  Purchase #4 $56.43   11.712%   $63.0391   $63.04   $63.05   $63.00  
  Purchase #5 $13.36   5.802%   $14.1351   $14.14   $14.15   $14.10  
  Purchase #6 $156.81   5.479%   $165.4016   $165.40   $165.40   $165.40  
  Purchase #7 $35.74   11.409%   $39.8176   $39.82   $39.80   $39.80  
  7 purchase totals = $798.94       $858.9395   $858.95   $858.95   $858.80