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 $65.36   13.165%   $73.9646   $73.96   $73.95   $74.00  
  Purchase #2 $219.36   11.683%   $244.9878   $244.99   $245.00   $245.00  
  Purchase #3 $97.52   11.591%   $108.8235   $108.82   $108.80   $108.80  
  Purchase #4 $238.49   4.761%   $249.8445   $249.84   $249.85   $249.80  
  Purchase #5 $136.72   5.162%   $143.7775   $143.78   $143.80   $143.80  
  Purchase #6 $181.36   4.278%   $189.1186   $189.12   $189.10   $189.10  
  Purchase #7 $205.95   6.614%   $219.5715   $219.57   $219.55   $219.60  
  7 purchase totals = $1,144.76       $1,230.0880   $1,230.08   $1,230.05   $1,230.10