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 $82.65   11.494%   $92.1498   $92.15   $92.15   $92.10  
  Purchase #2 $218.91   3.221%   $225.9611   $225.96   $225.95   $226.00  
  Purchase #3 $58.95   13.125%   $66.6872   $66.69   $66.70   $66.70  
  Purchase #4 $60.55   7.690%   $65.2063   $65.21   $65.20   $65.20  
  Purchase #5 $246.80   8.667%   $268.1902   $268.19   $268.20   $268.20  
  Purchase #6 $106.93   8.424%   $115.9378   $115.94   $115.95   $115.90  
  Purchase #7 $161.52   8.127%   $174.6467   $174.65   $174.65   $174.60  
  7 purchase totals = $936.31       $1,008.7791   $1,008.79   $1,008.80   $1,008.70