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 $228.94   11.118%   $254.3935   $254.39   $254.40   $254.40  
  Purchase #2 $160.31   8.760%   $174.3532   $174.35   $174.35   $174.40  
  Purchase #3 $142.84   6.679%   $152.3803   $152.38   $152.40   $152.40  
  Purchase #4 $181.34   9.697%   $198.9245   $198.92   $198.90   $198.90  
  Purchase #5 $23.59   6.683%   $25.1665   $25.17   $25.15   $25.20  
  Purchase #6 $168.55   9.338%   $184.2892   $184.29   $184.30   $184.30  
  Purchase #7 $246.96   13.304%   $279.8156   $279.82   $279.80   $279.80  
  7 purchase totals = $1,152.53       $1,269.3228   $1,269.32   $1,269.30   $1,269.40