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 $201.57   11.169%   $224.0834   $224.08   $224.10   $224.10  
  Purchase #2 $177.83   6.742%   $189.8193   $189.82   $189.80   $189.80  
  Purchase #3 $96.60   7.852%   $104.185   $104.19   $104.20   $104.20  
  Purchase #4 $84.54   5.110%   $88.86   $88.86   $88.85   $88.90  
  Purchase #5 $85.67   9.196%   $93.5482   $93.55   $93.55   $93.50  
  Purchase #6 $179.57   11.692%   $200.5653   $200.57   $200.55   $200.60  
  Purchase #7 $198.96   5.331%   $209.5666   $209.57   $209.55   $209.60  
  7 purchase totals = $1,024.74       $1,110.6278   $1,110.64   $1,110.60   $1,110.70