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 $41.57   13.661%   $47.2489   $47.25   $47.25   $47.20  
  Purchase #2 $240.88   12.436%   $270.8358   $270.84   $270.85   $270.80  
  Purchase #3 $28.39   10.761%   $31.445   $31.45   $31.45   $31.40  
  Purchase #4 $63.42   5.730%   $67.054   $67.05   $67.05   $67.10  
  Purchase #5 $72.29   13.359%   $81.9472   $81.95   $81.95   $81.90  
  Purchase #6 $94.44   9.694%   $103.595   $103.60   $103.60   $103.60  
  Purchase #7 $181.39   12.460%   $203.9912   $203.99   $204.00   $204.00  
  7 purchase totals = $722.38       $806.1171   $806.13   $806.15   $806.00