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 $207.46   13.604%   $235.6829   $235.68   $235.70   $235.70  
  Purchase #2 $121.73   6.778%   $129.9809   $129.98   $130.00   $130.00  
  Purchase #3 $155.83   7.504%   $167.5235   $167.52   $167.50   $167.50  
  Purchase #4 $18.35   13.607%   $20.8469   $20.85   $20.85   $20.80  
  Purchase #5 $32.25   7.755%   $34.751   $34.75   $34.75   $34.80  
  Purchase #6 $65.66   13.230%   $74.3468   $74.35   $74.35   $74.30  
  Purchase #7 $167.99   9.534%   $184.0062   $184.01   $184.00   $184.00  
  7 purchase totals = $769.27       $847.1382   $847.14   $847.15   $847.10