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 $68.91   13.258%   $78.0461   $78.05   $78.05   $78.00  
  Purchase #2 $237.53   8.182%   $256.9647   $256.96   $256.95   $257.00  
  Purchase #3 $11.52   11.579%   $12.8539   $12.85   $12.85   $12.90  
  Purchase #4 $231.39   4.278%   $241.2889   $241.29   $241.30   $241.30  
  Purchase #5 $203.34   12.553%   $228.8653   $228.87   $228.85   $228.90  
  Purchase #6 $246.60   8.819%   $268.3477   $268.35   $268.35   $268.30  
  Purchase #7 $25.69   6.443%   $27.3452   $27.35   $27.35   $27.30  
  7 purchase totals = $1,024.98       $1,113.7118   $1,113.72   $1,113.70   $1,113.70