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 $146.46   6.826%   $156.4574   $156.46   $156.45   $156.50  
  Purchase #2 $43.72   6.765%   $46.6777   $46.68   $46.70   $46.70  
  Purchase #3 $228.84   7.516%   $246.0396   $246.04   $246.05   $246.00  
  Purchase #4 $61.85   7.213%   $66.3112   $66.31   $66.30   $66.30  
  Purchase #5 $96.95   5.395%   $102.1805   $102.18   $102.20   $102.20  
  Purchase #6 $201.82   8.530%   $219.0352   $219.04   $219.05   $219.00  
  Purchase #7 $183.90   11.787%   $205.5763   $205.58   $205.60   $205.60  
  7 purchase totals = $963.54       $1,042.2779   $1,042.29   $1,042.35   $1,042.30