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 $189.56   10.651%   $209.75   $209.75   $209.75   $209.80  
  Purchase #2 $205.59   5.337%   $216.5623   $216.56   $216.55   $216.60  
  Purchase #3 $218.45   7.604%   $235.0609   $235.06   $235.05   $235.10  
  Purchase #4 $140.95   10.571%   $155.8498   $155.85   $155.85   $155.80  
  Purchase #5 $118.46   9.364%   $129.5526   $129.55   $129.55   $129.60  
  Purchase #6 $31.43   6.531%   $33.4827   $33.48   $33.50   $33.50  
  Purchase #7 $96.44   11.736%   $107.7582   $107.76   $107.75   $107.80  
  7 purchase totals = $1,000.88       $1,088.0165   $1,088.01   $1,088.00   $1,088.20