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 $45.29   13.813%   $51.5459   $51.55   $51.55   $51.50  
  Purchase #2 $161.58   11.584%   $180.2974   $180.30   $180.30   $180.30  
  Purchase #3 $77.96   3.638%   $80.7962   $80.80   $80.80   $80.80  
  Purchase #4 $175.29   11.545%   $195.5272   $195.53   $195.55   $195.50  
  Purchase #5 $180.91   13.148%   $204.696   $204.70   $204.70   $204.70  
  Purchase #6 $228.35   12.310%   $256.4599   $256.46   $256.45   $256.50  
  Purchase #7 $202.44   6.802%   $216.21   $216.21   $216.20   $216.20  
  7 purchase totals = $1,071.82       $1,185.5326   $1,185.55   $1,185.55   $1,185.50