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 $62.83   6.576%   $66.9617   $66.96   $66.95   $67.00  
  Purchase #2 $103.93   12.374%   $116.7903   $116.79   $116.80   $116.80  
  Purchase #3 $167.73   11.243%   $186.5879   $186.59   $186.60   $186.60  
  Purchase #4 $204.49   7.497%   $219.8206   $219.82   $219.80   $219.80  
  Purchase #5 $211.87   3.459%   $219.1986   $219.20   $219.20   $219.20  
  Purchase #6 $35.41   7.362%   $38.0169   $38.02   $38.00   $38.00  
  Purchase #7 $206.36   8.162%   $223.2031   $223.20   $223.20   $223.20  
  7 purchase totals = $992.62       $1,070.5791   $1,070.58   $1,070.55   $1,070.60