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 $213.54   12.140%   $239.4638   $239.46   $239.45   $239.50  
  Purchase #2 $82.97   13.427%   $94.1104   $94.11   $94.10   $94.10  
  Purchase #3 $109.44   10.368%   $120.7867   $120.79   $120.80   $120.80  
  Purchase #4 $233.55   10.111%   $257.1642   $257.16   $257.15   $257.20  
  Purchase #5 $118.98   12.281%   $133.5919   $133.59   $133.60   $133.60  
  Purchase #6 $203.79   4.248%   $212.447   $212.45   $212.45   $212.40  
  Purchase #7 $22.55   11.231%   $25.0826   $25.08   $25.10   $25.10  
  7 purchase totals = $984.82       $1,082.6466   $1,082.64   $1,082.65   $1,082.70