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 $195.52   4.755%   $204.817   $204.82   $204.80   $204.80  
  Purchase #2 $138.51   3.865%   $143.8634   $143.86   $143.85   $143.90  
  Purchase #3 $121.95   4.799%   $127.8024   $127.80   $127.80   $127.80  
  Purchase #4 $184.80   8.750%   $200.97   $200.97   $200.95   $201.00  
  Purchase #5 $82.64   8.568%   $89.7206   $89.72   $89.70   $89.70  
  Purchase #6 $191.29   7.708%   $206.0346   $206.03   $206.05   $206.00  
  Purchase #7 $23.96   3.715%   $24.8501   $24.85   $24.85   $24.90  
  7 purchase totals = $938.67       $998.0581   $998.05   $998.00   $998.10