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 $206.94   13.839%   $235.5784   $235.58   $235.60   $235.60  
  Purchase #2 $194.29   11.608%   $216.8432   $216.84   $216.85   $216.80  
  Purchase #3 $127.57   7.818%   $137.5434   $137.54   $137.55   $137.50  
  Purchase #4 $34.56   8.729%   $37.5767   $37.58   $37.60   $37.60  
  Purchase #5 $174.98   5.638%   $184.8454   $184.85   $184.85   $184.80  
  Purchase #6 $87.86   8.371%   $95.2148   $95.21   $95.20   $95.20  
  Purchase #7 $136.31   12.303%   $153.0802   $153.08   $153.10   $153.10  
  7 purchase totals = $962.51       $1,060.6821   $1,060.68   $1,060.75   $1,060.60