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 $219.53   6.629%   $234.0826   $234.08   $234.10   $234.10  
  Purchase #2 $172.47   4.533%   $180.2881   $180.29   $180.30   $180.30  
  Purchase #3 $52.95   11.351%   $58.9604   $58.96   $58.95   $59.00  
  Purchase #4 $57.87   4.234%   $60.3202   $60.32   $60.30   $60.30  
  Purchase #5 $214.89   6.319%   $228.4689   $228.47   $228.45   $228.50  
  Purchase #6 $146.28   9.815%   $160.6374   $160.64   $160.65   $160.60  
  Purchase #7 $122.34   6.685%   $130.5184   $130.52   $130.50   $130.50  
  7 purchase totals = $986.33       $1,053.2760   $1,053.28   $1,053.25   $1,053.30