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 $184.60   9.166%   $201.5204   $201.52   $201.50   $201.50  
  Purchase #2 $23.29   9.244%   $25.4429   $25.44   $25.45   $25.40  
  Purchase #3 $178.68   11.142%   $198.5885   $198.59   $198.60   $198.60  
  Purchase #4 $128.84   7.279%   $138.2183   $138.22   $138.20   $138.20  
  Purchase #5 $198.45   12.412%   $223.0816   $223.08   $223.10   $223.10  
  Purchase #6 $150.54   4.650%   $157.5401   $157.54   $157.55   $157.50  
  Purchase #7 $17.83   7.551%   $19.1763   $19.18   $19.20   $19.20  
  7 purchase totals = $882.23       $963.5681   $963.57   $963.60   $963.50