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 $192.52   5.257%   $202.6408   $202.64   $202.65   $202.60  
  Purchase #2 $122.37   3.654%   $126.8414   $126.84   $126.85   $126.80  
  Purchase #3 $35.67   5.814%   $37.7439   $37.74   $37.75   $37.70  
  Purchase #4 $112.60   9.341%   $123.118   $123.12   $123.10   $123.10  
  Purchase #5 $194.82   9.661%   $213.6416   $213.64   $213.65   $213.60  
  Purchase #6 $203.55   3.788%   $211.2605   $211.26   $211.25   $211.30  
  Purchase #7 $90.46   3.536%   $93.6587   $93.66   $93.65   $93.70  
  7 purchase totals = $951.99       $1,008.9049   $1,008.90   $1,008.90   $1,008.80