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 $61.76   13.200%   $69.9123   $69.91   $69.90   $69.90  
  Purchase #2 $205.78   10.272%   $226.9177   $226.92   $226.90   $226.90  
  Purchase #3 $212.76   8.497%   $230.8382   $230.84   $230.85   $230.80  
  Purchase #4 $110.97   9.286%   $121.2747   $121.27   $121.25   $121.30  
  Purchase #5 $150.58   6.267%   $160.0168   $160.02   $160.00   $160.00  
  Purchase #6 $223.55   13.582%   $253.9126   $253.91   $253.90   $253.90  
  Purchase #7 $213.65   8.220%   $231.212   $231.21   $231.20   $231.20  
  7 purchase totals = $1,179.05       $1,294.0843   $1,294.08   $1,294.00   $1,294.00