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 $57.98   4.727%   $60.7207   $60.72   $60.70   $60.70  
  Purchase #2 $197.52   3.720%   $204.8677   $204.87   $204.85   $204.90  
  Purchase #3 $230.93   4.375%   $241.0332   $241.03   $241.05   $241.00  
  Purchase #4 $173.51   11.470%   $193.4116   $193.41   $193.40   $193.40  
  Purchase #5 $82.29   13.147%   $93.1087   $93.11   $93.10   $93.10  
  Purchase #6 $165.66   4.337%   $172.8447   $172.84   $172.85   $172.80  
  Purchase #7 $68.67   11.191%   $76.3549   $76.35   $76.35   $76.40  
  7 purchase totals = $976.56       $1,042.3415   $1,042.33   $1,042.30   $1,042.30