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 $136.31   11.478%   $151.9557   $151.96   $151.95   $152.00  
  Purchase #2 $63.45   10.262%   $69.9612   $69.96   $69.95   $70.00  
  Purchase #3 $105.81   11.862%   $118.3612   $118.36   $118.35   $118.40  
  Purchase #4 $244.88   6.397%   $260.545   $260.55   $260.55   $260.50  
  Purchase #5 $153.57   11.645%   $171.4532   $171.45   $171.45   $171.50  
  Purchase #6 $155.73   11.784%   $174.0812   $174.08   $174.10   $174.10  
  Purchase #7 $136.78   13.796%   $155.6502   $155.65   $155.65   $155.70  
  7 purchase totals = $996.53       $1,102.0077   $1,102.01   $1,102.00   $1,102.20