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 $62.57   13.112%   $70.7742   $70.77   $70.75   $70.80  
  Purchase #2 $38.41   6.806%   $41.0242   $41.02   $41.00   $41.00  
  Purchase #3 $242.50   11.144%   $269.5242   $269.52   $269.50   $269.50  
  Purchase #4 $190.87   3.498%   $197.5466   $197.55   $197.55   $197.50  
  Purchase #5 $215.53   10.580%   $238.3331   $238.33   $238.35   $238.30  
  Purchase #6 $84.50   3.328%   $87.3122   $87.31   $87.30   $87.30  
  Purchase #7 $111.46   9.417%   $121.9562   $121.96   $121.95   $122.00  
  7 purchase totals = $945.84       $1,026.4707   $1,026.46   $1,026.40   $1,026.40